Type DL_TPR: Source Routing

For type DL_TPR devices, GLD implements minimal support
for source routing. Source routing enables a station that is sending a packet
across a bridged medium to specify (in the packet MAC header)
routing information that determines the route that the packet will take through
the network.

Functionally, the source routing support provided by GLD learns routes,
solicits and responds to requests for information about possible multiple
routes, and selects among available routes. It adds Routing Information
Fields to the MAC headers of outgoing packets
and recognizes such fields in incoming packets.

GLD's source routing support does not implement the full Route Determination Entity (RDE) specified in Section 9 of ISO 8802-2 (IEEE 802.2). However, it is designed to interoperate
with any such implementations that might exist in the same (or a bridged)
network.